Nonequivalence of ³H- and ³²P-labeled diisopropylfluorophosphate for the study of granulocyte kinetics

Leukocyte kinetic studies that utilized autologous granulocytes double labeled in vitro with DF³²P and ³H-DFP have demonstrated that the two forms are not equivalent. Specific activities obtained with DF³²P-labeled cells are greater than with ³H-DFP-labeled cells. This is probably due to loss of a portion of the ³H label through metabolism of the isopropyl moiety in labeled cells in vivo. A fraction of this moiety may also be involved in lipid synthesis and thus be transiently retained in the cell. The data indicate that DF³²P is preferable to ³H-DFP as a cell label for the study of granulocyte kinetics and that the use of ³H-DFP may give rise to erroneous results.